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• How to preserve data integrity while minimizing the transmission size

  - by user1500578

  we have sensors in the wild that send their data to a server every day via TCP/IP, either through 3G or through satellite for the physical layer. The sensors can automatically switch from one to the other depending on their location and the quality of the signal with the local 3G operator. Given that the 3G and satellite communications are very expensive, we want to minimize the amount of data to send. But also, we want to protect ourselves from lost data. What would be the best strategy to ensure with reasonable certainty that the integrity of our data is preserved, while minimizing the amount of redundancy, i.e the amount of data transmitted ? I've read about the zfec codec, but I'm not sure if we need to transmit all the chunks, or if we need to send a hash code along each chunk.

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• Having an @ inside of a string - PHP

  - by Msencenb

  So I know that you use a backslash to escape most things in php however the @ symbol is an operator that suppresses error messages. I'm trying to put an email string like this inside of an array "[email protected]", however php is throwing an error. How do you escape the @ sign? EDIT: Here is the code example that was throwing the error: $arr = array(3=> "[email protected]",4=> "[email protected]"); However replacing the double quotes with single quotes fixes the error as answered below.... why is that true?

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• When does ref($variable) return 'IO'?

  - by Zaid

  Here's the relevant excerpt from the documentation of the ref function: The value returned depends on the type of thing the reference is a reference to. Builtin types include: SCALAR ARRAY HASH CODE REF GLOB LVALUE FORMAT IO VSTRING Regexp Based on this, I imagined that calling ref on a filehandle would return 'IO'. Surprisingly, it doesn't: use strict; use warnings; open my $fileHandle, '<', 'aValidFile'; close $fileHandle; print ref $fileHandle; # prints 'GLOB', not 'IO' perlref tries to explain why: It isn't possible to create a true reference to an IO handle (filehandle or dirhandle) using the backslash operator. The most you can get is a reference to a typeglob, which is actually a complete symbol table entry [...] However, you can still use type globs and globrefs as though they were IO handles. In what circumstances would ref return 'IO' then?

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• Does the JPQL avg aggregate function work with Integers?

  - by Kyle Renfro

  I have a JPA 2 Entity named Surgery. It has a member named transfusionUnits that is an Integer. There are two entries in the database. Executing this JPQL statement: Select s.transfusionUnits from Surgery s produces the expected result: 2 3 The following statement produces the expected answer of 5: Select sum(s.transfusionUnits) from Surgery s I expect the answer of the following statement to be 2.5, but it returns 2.0 instead. Select avg(s.transfusionUnits) from Surgery s If I execute the statement on a different (Float) member, the result is correct. Any ideas on why this is happening? Do I need to do some sort of cast in JPQL? Is this even possible? Surely I am missing something trivial here.

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• SQL Operators as text in where clause

  - by suggy1982

  I have the following table, which is used for storing bandings. The table is maintained via a web frontend. CREATE TABLE [dbo].[Banding]( [BandingID] [int] IDENTITY(1,1) NOT NULL, [ValueLowerLimitOperator] [varchar](10) NULL, [ValueLowerLimit] [decimal](9, 2) NULL, [ValueUpperLimitOperator] [varchar](10) NULL, [ValueUpperLimit] [decimal](9, 2) NULL, [VolumeLowerLimitOperator] [varchar](10) NULL The operator fields store values such as < = <=. I want to get to a position where I can use the operators values stored in the table in a case statement in a where clause. Like this. SELECT * FROM table WHERE CASE ValueLowerLimitOperator WHEN '<' THEN VALUE < X WHEN '>' THEN VALUE > X END rather than having to write mutiple case or if statements for each permutation. Does anyone have any suggestions how I can decode the operators values stored in the table as part of my query and then use them in a case/where statement?

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• Play 2.0 RESTful request post-processing

  - by virtualeyes

  In regard to this question I am curious how one can do post-request REST processing a la (crude): def postProcessor[T](content: T) = { request match { case Accepts.Json() => asJson(content) case Accepts.Xml() => asXml(content) case _ => content } } overriding onRouteRequest in Global config does not appear to provide access to body of the response, so it would seem that Action composition is the way to go to intercept the response and do post-processing task(s). Question: is this a good idea, or is it better to do content-type casting directly within a controller (or other class) method where the type to cast is known? Currently I'm doing this kind of thing everywhere: toJson( i18n("account not found") ) toJson( Map('orderNum-> orderNum) ) while I'd like the toJson/toXml conversion to happen based on accepts header post-request.

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• SQL Server Read Locking behavior

  - by Charles Bretana

  When SQL Server Books online says that "Shared (S) locks on a resource are released as soon as the read operation completes, unless the transaction isolation level is set to repeatable read or higher, or a locking hint is used to retain the shared (S) locks for the duration of the transaction." Assuming we're talking about a row-level lock, with no explicit transaction, at default isolation level (Read Committed), what does "read operation" refer to? The reading of a single row of data? The reading of a single 8k IO Page ? or until the the complete Select statement in which the lock was created has finished executing, no matter how many other rows are involved? NOTE: The reason I need to know this is we have a several second read-only select statement generated by a data layer web service, which creates page-level shared read locks, generating a deadlock due to conflicting with row-level exclusive update locks from a replication prcoess that keeps the server updated. The select statement is fairly large, with many sub-selects, and one DBA is proposing that we rewrite it to break it up into multiple smaller statements (shorter running pieces), "to cut down on how long the locks are held". As this assumes that the shared read locks are held till the complete select statement has finished, if that is wrong (if locks are released when the row, or the page is read) then that approach would have no effect whatsoever....

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• Problems installing Windows service via Group Policy in a domain

  - by CraneStyle

  I'm reasonably new to Group Policy administration and I'm trying to deploy an MSI installer via Active Directory to install a service. In reality, I'm a software developer trying to test how my service will be installed in a domain environment. My test environment: Server 2003 Domain Controller About 10 machines (between XP SP3, and server 2008) all joined to my domain. No real other setup, or active directory configuration has been done apart from things like getting DNS right. I suspect that I may be missing a step in Group Policy that says I need to grant an explicit permission somewhere, but I have no idea where that might be or what it will say. What I've done: I followed the documentation from Microsoft in How to Deploy Software via Group Policy, so I believe all those steps are correct (I used the UNC path, verified NTFS permissions, I have verified the computers and users are members of groups that are assigned to receive the policy etc). If I deploy the software via the Computer Configuration, when I reboot the target machine I get the following: When the computer starts up it logs Event ID 108, and says "Failed to apply changes to software installation settings. Software changes could not be applied. A previous log entry with details should exist. The error was: An operations error occurred." There are no previous log entries to check, which is weird because if it ever actually tried to invoke the windows installer it should log any sort of failure of my application's installer. If I open a command prompt and manually run: msiexec /qb /i \\[host]\[share]\installer.msi It installs the service just fine. If I deploy the software via the User Configuration, when I log that user in the Event Log says that software changes were applied successfully, but my service isn't installed. However, when deployed via the User configuration even though it's not installed when I go to Control Panel - Add/Remove Programs and click on Add New Programs my service installer is being advertised and I can install/remove it from there. (this does not happen when it's assigned to computers) Hopefully that wall of text was enough information to get me going, thanks all for the help.

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• Perfectly reproducable select statement default ordering issue....

  - by Dave

  Hi, I've recently been chasing an issue with a client's db... solution found, but impossible to recreate. Essentially, we're doing a Select * from mytable where ArbitraryColumn = 75 Where MyTable has an Identity column, called 'MyIndentityColumn' - incremented by one in each insert. Naturally, and normally I would assume that the order returned would be the order in which they are inserted (bad assumption, but one which was forced onto me, through an inherited application - which has been patched). Essentially, I would like suggestions as to why the database, when restored to my local machine (same OS, same SQL server version - 200 sp3) same collation, and same backup instance restored on it, as a test DB on the client site. When I perform the above select, I get them in order of insert (i.e. identity column ordered ascending). On the client, it seems random (but the same 'random' order each time)... A few other points: I have the same collation on my test server as client Same DB backup restored to a test only I can access Same SQL server version and service pack Same OS Test DB is a new DB - new log and MDF... I have the problem 'solved' by adding an explicit order by clause but I want to undertand the cause of the issue, given the exact nature of my attempts to recreate it beuing futile, and perfectly recreatable on the client server... Thanks in advance, Dave

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• Need a regular expression for an Irish phone number

  - by Eoghan O'Brien

  I need to validate an Irish phone number but I don't want to make it too user unfriendly, many people are used to writing there phone number with brackets wrapping their area code followed by 5 to 7 digits for their number, some add spaces between the area code or mobile operator. The format of Irish landline numbers is an area code of between 1 and 4 digits and a number of between 5 to 8 digits. e.g. (021) 9876543 (01)9876543 01 9876543 (0402)39385 I'm looking for a regular expression for Javascript/PHP. Thanks.

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• Within a Visual Studio 2008 Add-In, how can I tell which interfaces a class' property implements?

  - by Tim Stewart

  In a Visual Studio Add-In, I'm enumerating over the members of a class in the current source file. When I encounter a property (e.g. CodeElement.Kind == vsCMElement.vsCMElementProperty) I cast that CodeElement to a CodeProperty and I can see the property's name and type. What I'm having a problem with is getting a list of the property's implemented interfaces. I'm wondering if this is because the implemented interfaces might be in assemblies that Visual Studio doesn't "know" about. Is there a way to get the list of interfaces that a property implements? Thanks.

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• C++ fixed point library?

  - by uj2

  I am looking for a free C++ fixed point library (Mainly for use with embedded devices, not for arbitrary precision math). Basically, the requirements are: No unnecessary runtime overhead: whatever can be done at compile time, should be done at compile time. Ability to transparently switch code between fixed and floating point, with no inherent overhead. Fixed point math functions. There's no much point using fixed point if you need to cast back and forth in order to take a square root. Small footprint. Any suggestions?

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• Template type deduction with a non-copyable class

  - by Evan Teran

  Suppose I have an autolocker class which looks something like this: template <T> class autolocker { public: autolocker(T *l) : lock(l) { lock->lock(); } ~autolocker() { lock->unlock(); } private: autolocker(const autolocker&); autolocker& operator=(const autolocker&); private: T *lock; } Obviously the goal is to be able to use this autolocker with anything that has a lock/unlock method without resorting to virtual functions. Currently, it's simple enough to use like this: autolocker<some_lock_t> lock(&my_lock); // my_lock is of type "some_lock_t" but it is illegal to do: autolocker lock(&my_lock); // this would be ideal Is there anyway to get template type deduction to play nice with this (keep in my autolocker is non-copyable). Or is it just easiest to just specify the type?

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• How can I join on a CSV varchar?

  - by mgroves

  I have a varchar field that contains a string like "10,11,12,13". How can I use that CSV string to join to another table with those IDs? Here's the approach I'm taking now: select * from SomeTable a WHERE (',' + @csvString + ',') LIKE '%,' + CONVERT(varchar(25), a.ID) + ',%' Where @csvString is "10,11,12,...". I intend to use this method as a join condition as well. That method works, but it's rather slow (using CAST doesn't improve the speed). I understand that having CSVs in the database like that is usually a very silly idea in most cases, but there's nothing I can do about that.

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• Consing lists with user-defined type in Haskell

  - by user1319603

  I have this type I defined myself: data Item = Book String String String Int -- Title, Author, Year, Qty | Movie String String String Int -- Title, Director, Year, Qty | CD String String String Int deriving Show -- Title, Artist, Year, Qty I've created an empty list all_Items = [] With the following function I am trying to insert a new book of type Item (Book) into the all_Items addBook all_Items = do putStrLn "Enter the title of the book" tit <- getLine putStrLn "Enter the author of the book" aut <- getLine putStrLn "Enter the year this book was published" yr <- getLine putStrLn "Enter quantity of copies for this item in the inventory" qty <- getLine Book tit aut yr (read qty::Int):all_Items return(all_Items) I however am receiving this error: Couldn't match expected type `IO a0' with actual type `[a1]' The error points to the line where I am using the consing operator to add the new book to the list. I can gather that it is a type error but I can't figure out what it is that I am doing wrong and how to fix it. Thanks in Advance!

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• visual studio intellisense error

  - by rakkarage

  template <typename T> class Test { friend Test<T> & operator * (T lhs, const Test<T> & rhs) { Test<T> r(rhs); // return r *= lhs; } } 4 IntelliSense: identifier "T" is undefined why is T defined on line 3 but not line 4? i mean i guess its not a real error just an intellisense error... it works anyway but is there something wrong? can i fix it? or remove the red squiggles somehow? thanks i am using visual studio 2010... i wonder if this happens in other versions as well?

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• Can't return a String value and append it...why?

  - by squeezemylime

  I am writing an app and am having problems returning a simple string value, and I'm not sure why. The function I am using (within a file called APIManager.m) is: - (NSString*) returnVenueUrl { NSString *venueUrl = [devEnvironment stringByAppendingString:@"venue/id/"]; return venueUrl; } I can return this properly by doing this in another .m file: APIManager *apiManager = [APIManager apiManager]; NSLog(@"view venue URL is here: %@", [apiManager returnVenueUrl]); But when I go to append a variable cast as a String onto it, I get nothing.. venueURL = [apiManager returnVenueUrl]; venueURL = [venueURL stringByAppendingString:venueId]; NSLog(@"the Full Venue URL is: %", venueURL); If anyone has any advice on how to fix this, it would be much appreciated!

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• Reading in 4 bytes at a time

  - by alphomega

  I have a big file full of integers that I'm loading in. I've just started using C++, and I'm trying out the filestream stuff. From everything I've read, it appears I can only read in bytes, So I've had to set up a char array, and then cast it as a int pointer. Is there a way I can read in 4 bytes at a time, and eliminate the need for the char array? const int HRSIZE = 129951336; //The size of the table char bhr[HRSIZE]; //The table int *dwhr; int main() { ifstream fstr; /* load the handranks.dat file */ std::cout << "Loading table.dat...\n"; fstr.open("table.dat"); fstr.read(bhr, HRSIZE); fstr.close(); dwhr = (int *) bhr; }

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• Pointing to vectors

  - by Matt Munson

  #include <iostream> #include <vector> using namespace std; int main () { vector <int> qwerty; qwerty.push_back(5); vector <int>* p = &qwerty; cout << p[0]; //error: no match for 'operator<<' in 'std::cout << * p' } I'm generally unclear on how to use pointers with vectors, so I'm pretty mystified as to why this is not working. To my mind, this should print 5 to screen.

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• Problem at JUnit test with generics

  - by Tom Brito

  In my utility method: public static <T> T getField(Object obj, Class c, String fieldName) { try { Field field = c.getDeclaredField(fieldName); field.setAccessible(true); return (T) field.get(obj); } catch (Exception e) { e.printStackTrace(); fail(); return null; } } The line return (T) field.get(obj); gives the warning "Type safety: Unchecked cast from Object to T"; but I cannot perform instanceof check against type parameter T, so what am I suppose to do here?

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• rails - Redirecting console output to a file

  - by egarcia

  On a bash console, if I do this: cd mydir ls -l > mydir.txt The operator captures the standard input and redirects it to a file; so I get the listing of files in mydir.txt instead of in the standard output. Is there any way to do something similar on the rails console? I've got a ruby statement that generates lots of prints (~8k lines) and I'd like to be able to see it completely, but the console only "remembers" the last 1024 lines or so. So I thought about redirecting to a file - If anyone knows a better option, I'm all ears.

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• DataSet with many OR clauses

  - by Silvan

  Hello :) I've got a little problem with a query which I create in the Visual Studio Designer. I need a query with a lot of 'OR'-clauses for the same column. I found the operator 'IN', but I don't know how to use that in the Visual Studio Designer: Example IN: SELECT EmployeeID, FirstName, LastName, HireDate, City FROM Employees WHERE City IN ('Seattle', 'Tacoma', 'Redmond') I tried to do it in this way: SELECT [MachineryId], [ConstructionSiteId], [DateTime], [Latitude], [Longitude], [HoursCounter] FROM [PositionData] WHERE [MachineryID] IN @MachineryIDs But this doesn't work. Is there another way to handle a lot of OR clauses? Thank you very much for your help.

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• SQL vs MySQL: Rules about aggregate operations and GROUP BY

  - by Phazyck

  In this book I'm currently reading while following a course on databases, the following example of an illegal query using an aggregate operator is given: Find the name and age of the oldest sailor. Consider the following attempt to answer this query: SELECT S.name, S.age FROM Sailors.S The intent is for this query to return not only the maximum age but also the name of the sailors having that age. However, this query is illegal in SQL--if the SELECT clause uses an aggregate operation, then it must use only aggregate operations unless the query contains a GROUP BY clause! Some time later while doing an exercise using MySQL, I faced a similar problem, and made a mistake similar to the one mentioned. However, MySQL didn't complain and just spit out some tables which later turned out not be what I needed. Is the query above really illegal in SQL, but legal in MySQL, and if so, why is that? In what situation would one need to make such a query?

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• JBoss 4.2.3 Servlet API 2.5 JSF 2.0 Hibernate 3.0 Support Added [Solved]

  - by AZ_

  While deploying my project on Redhat 6 with Jboss 4.2.3 I was having following difficulties so I decided to put it on stackoverflow so that it can help other people. If anyone could suggest a good title so that it can easily be searched, please Q: How to make Jboss 4.2.x to ignore old JSF libraries and use one within your project libs? Q: How to make Jboss scan specific path for WAR file scanning? Q: How to bind Jboss with IP address rather then localhost? Q: Where Jboss put exploded WAR file? Q: Hibernate-annotations conflict with Jboss 4.2.3 annotations and throwing following Exception. java.lang.ClassCastException: org.hibernate.validator.event.ValidateEventListener cannot be cast to org.hibernate.event.PreInsertEventListener Q: How to run JSF 2.0.x on JBoss 4.0.x ? As JSF 2.0 supports at least Servlet 2.5 API and JBoss has Tomcat 5.x that can support Servlet 2.4 at max. Q: How to change Servlet version of a Dynamic Web Project?

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• How do I make a class whose interface matches double, but upon which templates can be specialized?

  - by Neil G

  How do I make a class whose interface matches double, but whose templated types do not dynamic cast to double? The reason is that I have a run-time type system, and I want to be able to have a type that works just like double: template<int min_value, int max_value> class BoundedDouble: public double {}; And then inherit use template specialization to get run-time information about that type: template<typename T> class Type { etc. } template<int min_value, int max_value> class Type<BoundedDouble<min_value, max_value>> { int min() const { return min_value; } etc. } But, you can't inherit from double...

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